Modification of drawn film

ABSTRACT

The Invention relates to a drawn polymer film, comprising (A) a polymer or polymer blend and at least (B) one additional component with an average particle diameter of between 0.1 and 15 μm, which by means of (C) one or several secondary treatment steps is processed to form a membrane after being drawn. The average particle diameter of component (B) ranges between 0.1 and 15 μm, preferably 0.5-8.0 μm, with the range between 1.0 and 7.0 μm being particularly preferred. The membranes are used for alkene-alkane separation, electrodialysis, the desalinisation of seawater, in fuel cell applications and other membrane applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/477,174, filed Jan. 9, 2004, which is a 35 U.S.C. 371 nationalstage application of PCT/EP2002/005256, filed May 13, 2002, which claimspriority of German Application No. 10122814.7 filed on May 11, 2001, allof which are incorporated herein by reference.

STATE-OF-THE-ART

Already since more than 20 years stretched films are used in technology.Polypropylene or polyethylene films formed by extrusion are widely usedin applications such as food packaging, food container and the like.Stretched polypropylene films, particularly biaxially stretchedpolypropylene films are widely used in packaging materials for theirexcellent mechanical and optical properties. They are produced generallyby successive biaxial stretching using a tenter.

Recently stretched foils with inorganic bulking agents are used asbreathable foils for diaper film. The pore diameter of commonlyemployed, very economical films however is too big by orders ofmagnitude, in that these foils could find use for applications whichrequire dense membranes, such as for use in a fuel cell.

OBJECT OF THE PRESENT INVENTION

It is the object of the present invention to produce economicallymembranes based on stretched films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process for forming a drawn composite film havingparticle components and pores or cavity formed around the particlecomponents, in accordance with the present invention.

FIG. 2 shows schematically intercalation of a dye molecule into thecavities of a phyllosilicate particle.

DESCRIPTION OF THE INVENTION

The present invention concerns membranes based on stretched films.

The above task can be resolved according to the present invention by astretched polymer film, comprising (A) a polymer or polymer blend and atleast (B) another component with an average particle diameter of 0.1 to15 μm, which (C) by one or more posttreatment steps is processed afterthe stretching to a membrane.

It has now been found that you cannot process without the stretching thefoil consisting of the polymer (A) and the particle-shaped component(B), at the same posttreatment steps (C) to a membrane with the sameproperties.

The average particle diameter of the component (B) is in the range of0.1-15 μm. Preferred is 0.5-8.0 μm and particularly preferred is therange of 1.0-7.0 μm. If the diameter is smaller than 0.1 μm, a secondaryagglomeration results and the resulting particles have partly bigdiameters which usually lead to a tearing of the foil in the stretchingprocess. With regard to the form of the particles there is no specialrestriction. However, spherical particles are preferred.

Before the stretching the amount of the component (B) of thenon-stretched foil is 2 to 80% by weight, 10 to 70% by weight arepreferred and 20 to 60% by weight are preferred particularly. The weightproportion of the polymer component (A) is correspondingly 98 to 20% byweight before the stretching, 90 to 30% by weight are preferred and 80to 40% by weight are preferred particularly.

There is no particular restriction as to the method by which theparticle-shaped component (B) is incorporated into the polymer component(A). Said method includes a simple mixing method. The mixing process canbe carried out by adding the component (B) into the melted component(A). The mixing process can take place by use of a screw extrusionkneader (e.g. a single-screw extruder or a twin-screw extruder), aBanbury mixer, a continuous mixer, a mixing roll, or the like. When thecomponent (A) can not be melted or when it is not desired, it isdissolved in a suitable solvent or solvent mixture. Suitable is anysolvent that dissolves the component (A) and which is at the same timenot a solvent for the component (B). Preferred solvents are water andaprotic solvents, such as tetrahydrofurane (THF), dimethylsulfoxide(DMSO), N-methylpyrrolidone (NMP), sulfolane and dimethylacetamide(DMAc). The component (B) is then finely dispersed in the dissolvedcomponent (A).

In all cases of the mixing process a composite results.

With the use of solvents these must be removed again after drawing of afilm on a suitable underlay in a drying or precipitation process. Thisis state-of-the-art and for example described in PCT/EP 00/03910 and WO01/87992. The received foil represents a composite foil or compositmembrane. The component (B) is dispersed in the matrix of the component(A). If the crystallinity of the used polymer in the non-stretched filmis so great that the film in the dried state can not be stretched, thenthe solvent is not completely removed. It was surprisingly noticed thatfoils consisting of the components (A) and (B) which were produced by asolvent process with a following drying process and which are notstretchable in the dried state are very well stretchable withoutdestruction with a residual solvent concentration. The stretching iscarried out after this in a temperature range which is over the meltingpoint and below the boiling point of the solvent remaining into themembrane. Another solvent-free stretching process can follow thisstretching procedure.

The residual solvent concentration of the non-stretched foil is between2 and 30% by weight, particularly preferred is the range between 5 and20% by weight of solvent in the non-stretched foil.

The stretched composite film of the present invention may be subjectedas necessary before or after the follow-up treatment (C) to surfacetreatments, such as corona discharge, plasma treatment, and the like, atone or both sides. The stretched composite film of the present inventionmay be coated or laminated before or after the post treatment (C) on oneor both two sides with solvent or solvent-free with a layer of a polymeror a polymer mixture which carries if necessary functional groups.Indicate functional groups.

In the case, that the component (A) can be melted indestructibly, thestretched film containing the components (A) and (B), not yetposttreated with the procedure (C), can be produced by a known processwithout any restriction. The production of a stretched composite filmcan be conducted, for example, by a process which comprises subjecting acomposition of a fusible component (A), containing an at the sametemperature not fusible particle-shaped component (B) to melt extrusionby a T-die method and passing the extrudate through a cooling roll,combined with an air-knife or through nip rolls to form a film. Theproduction of a biaxially stretched film by successive biaxialstretching using a tenter is preferably conducted by a process whichcomprises forming a sheet or film from the above-mentioned compositionby a T-die method, an inflation method or the like, then feeding thesheet or film into a longitudinal stretching machine to conductlongitudinal stretching of 0.5- to 10-fold (expressed as a mechanicaldraw ratio). at a heating roll temperature of 100-380° C., preferred120-350° C. and particularly preferred 130-250° C., and subjecting themonoaxially stretched film to transversal stretching of 0.5- to 15-foldby the use of a tenter at a tenter temperature of 100-380° C., preferred120-350° C. and particularly preferred 130-250° C. The resultingbiaxially stretched film is further subjected, as necessary, to a heattreatment of 80-380° C. (in this heat treatment a transverse relaxationof 0-25% is allowed). Of course, further stretching may be conductedafter the above stretching. In the longitudinal stretching, it ispossible to combine multi-stage stretching, rolling, drawing, etc.Monoaxial stretching alone may be adopted to obtain a stretched film.

The particle-shaped component (B) can be organic or inorganic. It iscondition for the particle-shaped component (B) that an opening or avoid space forms around the preferably spherical particle in thefollowing stretching process (illus. 1). The preferably sphericalparticle is after the stretching process in a cavity or at anappropriate thickness of the film a pore has formed around theparticle-shaped component (B). If sufficient cavities border on eachother and their cross-sections overlap, a continuous way or path fromone side of the film to the other side results, what, at long last,represents again a pore, too. The component (B) remains after thestretching in the film.

A second path is created in the film through the stretching. The firstpath or the first phase represents the polymer (A) himself of which thefilm consists. The second path or phase is the cavities which havearisen from the stretching procedure. The particle-shaped component (B)is in the cavities. A continuous phase from one side to the other shallbe understood as a path. A real percolation must be possible so that theway or the phase is continuous. That is a permeating substance, a liquid(e.g. water), a gas or ion must be able to penetrate from one side tothe other side. If the cavity is filled, then the properties of the newpath are dependent on the “filler”. If the filler is ion conducting,then the complete path is ion conducting. It is important that the pathis continuous.

All inorganic substances which form layer structures or frameworkstructures are particularly preferred as particle-shaped component (B).Phyllosilicates and/or tectosilicates are particularly preferred. Allsynthetic and natural zeolites are preferred from the tectosilicates.

If the inorganic component (B) is a phyllosilicate, it is based onmontmorillonite, smectite, illite, sepiolite, palygorskite, muscovite,allevardite, amesite, hectorite, talc, fluorhectorite, saponite,beidellite, nontronite, stevensite, bentonite, mica, vermiculite,fluorvermiculite, halloysite, fluorine containing synthetical talc typesor blends of two, or more of the above-mentioned phyllosilicates. Thephyllosilicate can be delaminated or pillared. Particularly preferred isMontmorillonite. Furthermore preferred is the protonated form of thephyllosilicates and/or tectosilicates.

In one embodiment of the invention the component (B) which includeslayer structures and/or framework structures gets functionalized beforethe stretching and/or after the stretching. If the functionalizationhappens after the stretching, then it is a part of the post treatment(C). In a preferred embodiment the phyllosilicates and/or tectosilicatesget functionalized before or after the stretching.

Description of the Functionalized Phyllosilicate:

The term “a phyllosilicate” in general means a silicate, in which theSiO₄ tetraeders are connected in two-dimensional infinite networks. (Theempirical formula for the anion is (Si₂O₅ ²)_(n)). The single layers arelinked to one another by the cations positioned between them, which areusually Na, K, Mg, Al or/and Ca in the naturally occurringphyllosilicates.

By the term “a functionalized phyllosilicate or tectosilicate” weunderstand phyllosilicates or tectosilicates in which the layerdistances are at first increased via a intercalation of molecules byreaction with so-called functionalization agents. The layer thickness ofsuch silicates before delamination of molecules carrying functionalgroups is preferably 0.5 to 10 nm, more preferably 0.5 to 5 and mostpreferably 0.8 to 2.

To functionalize the phyllosilicates or tectosilicates, they are reacted(before or after production of the composites according to theinvention) with so-called functionalizing hydrophobization agents whichare often also called onium ions or onium salts. The insertion oforganic molecules often has a hydrophobization of the silicates as aconsequence, too. The expression functionalizing hydrophobization agentsis therefore used here.

The cations of the phyllosilicates or tectosilicates are replaced byorganic functionalizing hydrophobization agents in which by the natureof the organic rest the desired chemical functionalization can beadjusted inside and/or at the surface of the silicate. The chemicalfunctionalization depends on the kind of the respective functionalizingmolecule, oligomer or polymer, which is to be incorporated into thephyllosilicate.

The exchange of the cations usually of metal ions or protons can becomplete or partial. A complete exchange of the cations, metal ions orprotons is preferred. The quantity of the exchangeable cations, metalions or protons is usually expressed as milli equivalent (meq) per 1 gof phyllosilicate or tectosilicate and is referred to as ion exchangecapacity.

Preferred are phyllosilicates or tectosilicates having a cation exchangecapacity of at least 0.5, preferably 0.8 to 1.3 meq/g:

Suitable organic functionalizing hydrophobization agents are derivedfrom oxonium, ammonium, phosphonium and sulfonium ions, which may carryone or more organic residues.

As suitable functionalizing hydrophobization agents those of generalformula I and/or II are mentioned:

Where the substituents have the following meaning:

R1, R2, R3, R4 are independently from each other hydrogen, a straightchain, branched, saturated or unsaturated hydrocarbon radical with 1 to40, preferably 1 to 20 C atoms, optionally carrying at least onefunctional group or 2 of the radicals are linked with each other,preferably to a heterocyclic residue having 5 to 10 C atoms, morepreferably having one or more N atoms.

X represents phosphorous, nitrogen or carbon,

Y represents oxygen, sulfur or carbon,

n is an integer from 1 to 5, preferably 1 to 3 and

Z is an anion.

In case that Y represents carbon, one of the radicals R1, R2 or R3 isdouble bonded to this carbon.

Suitable functional groups are hydroxyl, nitro, phosphonic acid orsulfonic acid groups, whereas carboxyl and sulfonic acid groups areespecially preferred. In the same way sulfonic acid chloride andcarboxylic acid chlorides are especially preferred.

Suitable anions Z are derived from proton providing acids, in particularmineral acids, wherein halogens such as chlorine, bromine, fluorine,iodine, sulfate, sulfonate, phosphate, phosphonate, phosphite andcarboxylate, especially acetate are preferred.

The phyllosilicates and/or tectosilicates used as starting materials aregenerally reacted as a suspension. The preferred suspending agent iswater, optionally mixed with alcohols, especially lower alcohols having1 to 3 carbon atoms. If the functionalizing hydrophobization agent isnot water-soluble, then a solvent is preferred in which said agent issoluble. In such cases, this is especially an aprotic solvent. Furtherexamples for suspending agents are ketones and hydrocarbons. Usually asuspending agent miscible with water is preferred. On addition of thehydrophobizing agent to the phyllosilicate, ion exchange occurs wherebythe phyllosilicate usually precipitates from the solution. The metalsalt resulting as a by-product of the ion exchange is preferablywater-soluble, so that the hydrophobized phyllosilicate can be separatedas a crystalline solid, for example, by filtration. When thefunctionalization takes place after the stretching in the film, ofcourse the phyllosilicate or tectosilicate is available as a solidbefore the functionalization. The cation exchange is made by secondarytreatment of the stretched film in a solution containing thefunctionalizing substances. The removal of the cations originally boundto the silicate is carried out either with the same solvent or with asuitable other solvent in a second step. It is also possible to fix thecations originally bound to the silicate as a solid, particularly as ahardly soluble salt in and at the silicate surface. This is frequentlythe case when the cation bound originally at the silicate is a two,three or quadrivalent cation, particularly metal cation. Examples of itare Ti4+, Zr4+, ZrO2+ and TiO2+.

The ion exchange is mostly independent from the reaction temperature.The temperature is preferably above the crystallization point of themedium in which the functionalizing substances are, and below theboiling point thereof. For aqueous systems the temperature is between 0and 100° C., preferably between 40 and 80° C.

As functionalizing substances alkylammonium ions are preferred, inparticular if as a functional group additionally a carboxylic acidchloride or sulfonic acid chloride is present in the same molecule. Thealkylammonium ions can be obtained via usual methylation reagents suchas methyl iodide. Suitable ammonium ions are alpha-omega-aminocarboxylicacids, especially preferred are

Additional preferred ammonium ions are pyridine and laurylammonium ions.After functionalization the layer distance of the phyllosilicates is ingeneral between 1 to 5 nm, preferably 1.3 to 4 nm.

The hydrophobized and functionalized phyllosilicate is freed of water bydrying. In general a thus treated phyllosilicate still contains aresidual water concentration of 0-5% by weight of water. Thefunctionalized phyllosilicate can then be mixed as a suspension in asuspending agent as anhydrous as possible with the mentioned polymersand be reprocessed to a film. In case the extrusion is chosen to obtainthe non-stretched foil, the functionalized phyllosilicate ortectosilicate can be added to the melt. Preferred is the addition ofunmodified phyllosilicates or tectosilicates to the melt and afunctionalization of the silicates after the stretching. This isespecially preferred if the extrusion temperature lies over thedestruction temperature of the functionalizing substances.

An especially preferred functionalization of the tectosilicates and/orphyllosilicates is carried out with modified dyes or their precursors,particularly with triphenyl methane dyes. They have the

general formula:

In the present invention dyes are used which are derived from thefollowing basic structure:

The radicals R can be independently of each other hydrogen, a groupshowing 1 to 40 carbon atoms, preferably a branched or non branchedalkyl, cycloalkyl- or an optionally alkylated aryl group, these containif necessary one or more flourine atoms. The radicals R can correspondindependently of each other to the radicals R1, R2, R3 or R4 with thefunctional groups from the general formula (I) and (II) mentioned abovefor functionalizing hydrophobation agents.

To functionalize the phyllosilicate, the dye or its reduced precursor isreacted with the silicate in an aprotic solvent (e.g. tetrahydrofurane,DMAc, NMP). After approx. 24 hours the dye or the precursor isintercalated into the cavities of the phyllosilicate. The intercalationmust be such, that an ion conducting group is located on the surface ofthe silicate particle.

FIG. 2 shows schematically the process.

The so functionalized phyllosilicate is added as a supplement to thepolymer solution as described in application DE10024575.7. Thefunctionalization of the phyllosilicates or tectosilicates can be againcarried out via a cation exchange in the stretched film. It has provedto be especially favorable to use the preliminary stage of the dyes. Theactual dyes are formed by separation of water only in a followingoxidation by an acidic secondary treatment.

It was surprisingly noticed in the case of the triphenyl methane dyesthat a proton conductivity is supported in the membranes produced fromthat. Whether it even is an anhydrous proton conductivity cannot be saidwith sufficient safety. When the dyes are not bound to the silicate sothey are present in a free form inside the stretched membrane, theybleed out already after short

time with the reaction water in the fuel cell.

According to the invention the polymer mixtures containing sulfinategroups of the above mentioned parent application, especially preferablythe thermoplastic functionalized polymers (ionomers) are added to thesuspension of the hydrophobized phyllosilicates. This can be done usingalready dissolved polymers or the polymers are dissolved in thesuspension itself. Preferably the ratio of the phyllosilicates isbetween 1 and 70% by weight, more preferably between 2 and 40% by weightand most preferably between 5 and 15% by weight.

Another improvement compared with the parent application is theadditional addition of zirconium oxychloride (ZrOCl2) in the membranepolymer solution and in the cavities of the phyllosilicates and/ortectosilicates. If the secondary treatment of the membrane is carriedout in phosphoric acid, hardly soluble zirconium phosphate is thenprecipitated in an immediate proximity of the silica particle in themembrane. Zirconium phosphate exhibits a self-proton conductivity in theoperation of the fuel cell. The proton conductivity functions byformation of hydrogen phosphates as intermediate steps and isstate-of-the-art. The selective incorporation in a direct proximity to awater reservoir (silicates) is new.

The stretched, micro porous film containing a particle-shaped component(B) is subjected according to the present invention one or moresecondary treatments (C). In a special embodiment of the invention, themicro porous foil contains phyllosilicates and/or tectosilicates. Thesewill be functionalized now in one or several steps.

If the functionalized bulking agent, particularly zeolites andrepresentatives of the beidellite group and bentonites, is the only ionconducting component, then its weight proportion is generally between 5to 80%, preferably between 20 and 70% and most preferably in the rangeof 30 to 60% weight.

The polymers components of the component (A) of the composite membranesof the present invention are defined as follows:

(1) Main Chains (Backbones) of the Polymer of the Present Invention:

Actually all polymers are possibly as polymer main chains. Preferred asmain chains are, however:

-   -   Polyolefines like polyethylene, polypropylene, polyisobutylene,        polynorbonene, polymethylpentene, poly(1,4-isoprene),        poly(3,4-isoprene), poly(1,4-butadiene), poly(1,2-butadiene)    -   Styrene(co)polymer like polystyrene, poly(methylstyrene),        poly((α,β,β-trifluorostyrene), poly(pentafluorostyrene)    -   perflourinated ionomer like Nafion or the SO₂Hal-precursor of        Nafion Cl, Br, I), Dow membrane, GoreSelect membrane.    -   N-basic polymer like polyvinylcarbazole, polyethyleneimine,        poly(2-vinylpyridine), poly(3-vinylpyridine),        poly(4-vinylpyridine)    -   (Het) aryl main chain polymers which contain the structural        patterns listed in illus. 1.

(Het) aryl main chain polymers are preferred particularly as:

-   -   Polyetherketones like polyetherlketone PEK Victrex,        polyetheretherketone PEEK Victrex, polyetheretherketoneketone        PEEKK, polyetherketoneetherketone ketone PEKEKK Ultrapek    -   Polyethersulfones like polysulfone Udel, polyphenylsulfone Radel        R, Polyetherethersulfone Radel A, polyethersulfone PES Victrex    -   Poly(Benz) imidazole like PBI Celazol and others the (Benz)        imidazole-group containing oligomers and polymers, in which the        (Benz) imidazole group can be available in the main chain or in        the polymer lateral chain    -   Polyphenyleneether like e.g. poly(2,6-dimethyloxyphenylene),        poly(2,6-diphenyloxyphenylene)    -   Polyphenylenesulfide and copolymers    -   Poly(1,4-phenylene) or Poly(1,3-phenylene), which can be        modified in the lateral. group if necessary with benzoyl,        naphtoyl or o-phenyloxy-1,4-benzoyl group,        m-phenyloxy-1,4-benzoyl group or p-phenyloxy-1,4-benzoyl group.    -   Poly(benzoxazole) and copolymers    -   Poly(benzthiazole) and copolymers    -   Poly(phtalazinone) and copolymers    -   Polyaniline and copolymers    -   Polythiazole    -   Polypyrrole        (2) Polymer of the Type A (Polymer with Cation Exchange Group or        the Non-Ionic Precursors):

The polymer type A comprises all polymers which consist of theabove-mentioned polymer main chains (1) and the following cationexchange groups or their non-ionic precursors:

SO₃H, SO₃Me; PO₃H₂, PO₃Me₂; COOH, COOMe

SO₂X, POX₂, COX with X═Hal, OR₂, N(R₂)₂, anhydride radical, N-imidazolradical, N-pyrazole radical)

Preferred as functional groups are SO₃H, SO₃Me; PO₃H₂, PO₃Me₂ or SO₂X,POX₂. The strongly acidic sulfonic acid groups or their non-ionicprecursors are particularly preferred as functional groups. As polymermain chains aryl main chain polymers are preferred. Poly(etherketone)and poly(ethersulfone) are particularly preferred.

(3) Polymers of the Type B (Polymers with Iv-Basic Groups and/or AnionExchange Groups):

The polymer type B comprises all polymers which consist of theabove-mentioned polymer main chains (1) and carry the following anionexchange groups or their non-ionic precursors (with primary, secondary,tertiary basic N):

N(R₂)₃+Y—, P(R₂)₃+Y, whereby the R.sub.2 radicals can be the same ordifferent from each other;

N(R₂)₂ (primary, secondary or tertiary amines);

Polymers with the N-basic (her) aryl and heterocyclic groups shown inillus. 2.

As polymer main chains (het) aryl main chain polymers likepoly(etherketone), poly(ethersulfone) and poly(benzimidazole) arepreferably. As basic groups, primary, secondary and tertiary aminogroups, pyridine group and imidazole group are preferred.

(4) Polymers of the Type C Polymers with Cross-Linking Groups LikeSulfinate Group and/or Unsaturated Groups):

The polymertyp C comprises all polymers which consist of theabove-mentioned polymer main chains (1) and cross-linking groups.Cross-linking groups are, for example:

4 a) Alkene groups: Polymer C(R₁₃)═C(R₁₄R₁₅) with R₁₃, R₁₄, R₁₅═R₂ or R₄

4 b) Polymer Si (R₁₆R₁₇) H with R₁₆, R₁₇═R₂ or R₄

4 c) Polymer-COX, polymer-SO₂X, polymer-POX₂

4 d) Sulfinate group polymer-SO₂Me

4 e) Polymer N(R₂)₂ with R₂≠H.

One of the mentioned cross-linking groups or several of the mentionedcross-linking groups can lie on the polymer main chain. Thecross-linking can be carried out by the following literature knownreactions:

-   -   (I) Group of 4 a) by addition of peroxides;    -   (II) Group of 4 a) with group of 4 b) under Pt catalysis via        hydrosilation;    -   (III) Group 4d) with dihalogenalkane or dihalogenaryl        crosslinkers (for e.g. Hal-(CH₂)_(x)—Hal, x=3-20) with        S-alkylation of the sulfinate group;    -   (IV) Group 4e) with dihalogenalkane or dihalogenrryl        crosslinkers (for e.g. Hal-(CH₂)-Hal, x=3-20) with alkylation of        the tertiary basic N-group    -   (V) Group 4d) and group 4e) with dihalogenalkane or        dihalogenaryl crosslinkers (for e.g. Hal-(CH₂)_(x)—Hal, x=3-20)        with S-alkylation of the sulfinate group and alkylation of the        tertiary basic N—    -   (VI) Group of 4 c) by reaction with diamines.

The cross-linking reactions (III) and (IV) and (V) are preferred,particularly the cross-linking reaction (III).

(5) Polymers of the Type D (Polymers with Cation Exchange Groups andAnion Exchange Groups and/or Basic N Groups and/or Cross-LinkingGroups):

The polymertyp D comprises polymers which contain the above-mentionedpolymer main chains (1) and which can carry miscellaneous groups: thecation exchange group listed in (2) or their non-ionic precursor and theanion exchange group listed in (3) or primary, secondary or tertiaryN-basic groups and/or the cross-linking groups listed in (4).

The following combinations are possible:

Polymer D1: Polymer with cation exchange groups or their non-ionicprecursors and with anion exchange groups and/or N-basic groupsPolymer D2: Polymer with cation exchange groups or their non-ionicprecursors and with cross-linking groupsPolymer D3: Polymer with anion exchange groups and/or N-basic groups andwith cross-linking groupsPolymer D4: Polymer with cation exchange group or their non-ionicprecursors and with anion exchange groups and/or N-basic groups and withcross-linking groups

In the following will be described how stretched films containing aninorganic particle-shaped component (B) will be posttreated such thatmembranes are available for fuel cell applications, alkene alkaneseparation, electrodialysis, reverse osmosis, dialysis, pervaporation,electrolysis and other membrane applications.

A fusible stretchable polymer e.g. polypropylene is compounded with aninorganic particle-shaped component (B), preferably a componentcontaining layer structures and/or framework structures, particularly aphyllosilicate and/or tectosilicate with an average particle size of5-10μ. By compounding is understood: The polymer is intimately mixed ina melt state with the inorganic component, here, the silicate. A commonmethod is mixing the components in the twin-screw extruder. As a resultone obtains a composite, here silicate into polypropylene. The bentonitemontmorillonite is used exemplarily as a silica containing componentsubsequently. However, this does not mean any special restriction onbentonites.

The film is stretched now according to known methods as describedfurther above.

The stretched foil represents now a micro porous membrane. The pore sizeis dependent on the grain size, elongation properties of the polymer andof the tractive forces which were used during the stretching. As a densemembrane it is completely useless. Gasses e.g. penetrate roughlyunhindered through.

For the membranes of the present invention organically modified clay orzeolite is used. Bentonites are clays and montmorillonite is a specialbentonite. Montmorillonite is preferred. However, all other substratesinto which low molecular compounds can intercalate can also be used.Montmorillonite is able to tie molecules to itself by intercalation.Montmorillonite is modified such that a strongly basic component jutsout of the particle or is on the particle surface. This organicmodification is prior art. The organic component is preferablycontaining nitrogen. Heterocycles are particularly preferred and amongthose imidazoles and guanidine derivatives. This shall not mean anyrestriction to these two substance classes. Every other substance classwhich contains a strong endstanding base is also possible.

This organically modified montmorillonite is compounded with thepolymer, extrudated to a foil and after that stretched. In the case ofpolypropylene, up to 70% by weight can be easily incorporated.Particularly preferred are 50-60% by weight. As a result a micro porousstretched film with clay particle is obtained which carries imidazolegroups on its surface. This film is now posttreated with phosphoricacid. The phosphoric acid penetrates into the film and forms a compoundwith the imidazole groups. Furthermore still existing cavities both inthe inorganic particle and outside are filled with phosphoric acid. Thefilm has become now a dense proton-conducting membrane and is alreadyusable in this condition in a fuel cell such as.

To seal up further the membrane against the “bleeding” of the phosphoricacid, the membrane is dipped into zirconium oxychloride solutionaccording to the present invention. An insoluble zirconium phosphate isprecipitated at the phase boundary to the membrane and in the membraneitself. The membrane is further sealed up by this process. Zirconiumphosphates support proton conductivity. This membrane is suitable foruse in the fuel cell.

When using thermoplastics as a polymer component, such as polysulfone orVectra 950 (of Ticona), the membrane formed from it is applicable forthe PEM fuel cell. Also for temperatures above 80° C.

It is the advantage of the procedure of the present invention that thefilm is extruded and is not drawn out of a solvent.

The above-mentioned procedure with a polymer stretched to a film,organically modified clay, imidazole, phosphoric acid and after thatpartial precipitation to zirconium phosphate is only an exemplaryspecial example of the fundamental invention.

A second path is created in the film through the stretching. The polymercomponent (A) of which the film consists represents the first pathitself The cavities or the pores which have arisen from the stretchingprocedure are the second path. As a path a continuous way from one sideto the other shall be understood. A real percolation must be possible sothat the way is continuous. That is water vapor e.g. must be able topenetrate from one side to the other side. If the cavity is filled, thenthe properties of the new path are dependent on the “filler”. If thefiller is ion conducting, then the complete path is ion conducting. Itis important that the path is continuous. The film before the stretchingcan be produced by extrusion. However, it is also possible to producethe film out of a solvent.

The production of the film with the modified or unmodified bulking agentout of a solvent is prior art.

The extrusion presupposes a melting of the polymer. Most of thefunctionalized polymers can not be extruded without considerabledisadvantages. If the polymer contains sulfonic acid groups or chemicalprecursors like sulfochlorides, it degenerates before it melts. In suchcases the production is preferred through a solvent containing process.

The properties of the two paths can be modified over an almost arbitraryrange. It is a problem in fuel cell engineering that proton conductivityworks below 80° C. with hydrated membranes works particularly well (e.g.Nafion). Above this temperature water is lost increasingly and theproton conductivity and with that the performance drops as aconsequence. According to prior art it has been attempted to solve thisproblem by producing composite materials from a polymer and an inorganicbulking agent which is also proton conducting or supports protonconductivity. The problem is that the individual paths, that isinorganic bulking agent or organic ionomer are not independently of eachother continuous from one side of the membrane to the other side of themembrane.

Stepping up from prior art and according to the present invention amembrane is produced. It contains a water-dependent polymericproton-conductor, e.g. a polymeric sulfonic acid and an inorganiccomponent which, if necessary, has been organically modified before.This film is now stretched and the resulting second path is filled withan at higher temperature T>80° C.) proton conducting substance. Thefilling can be obtained e.g. by alternating post-treatment of themicroporous membrane in phosphoric acid and zirconium oxychloride(ZrOCl2). This process can be repeated so often until no furtherzirconium phosphate precipitates in the membrane. However, theprecipitation of zirconium phosphate is only one possibility. E.g. asulfonated polyetherketone or polysulfone is used as polymer.

As a result one gets a membrane which has two continuous protonconducting paths. Below 80° C. the proton conductivity workspredominantly through polymer sulfonic acid swollen in water and in thetemperature range above through the inorganic proton conductor. A fluenttransition takes place.

In another embodiment the concept of the two paths is reduced to anunfinished microporous membrane which is adapted in a secondmodification step to the desired application. There are two membraneswhich are joined together to one without that they disturb themselves intheir membrane function. Another clear picture is a textile substancewoven from two threads with different color. Whereby the threads can bechosen in a very broad range. However, one of the threads is inserted inthe finished homogeneous fabric afterwards.

The procedure is exemplarily once again schematically described in theparticular preferably case, that the component (A) is a withoutdegradation fusible polymer and that the particle-shaped component (B)is a phyllosilicate or tectosilicate with an average size of 0.1 to 15μ.

A microporous film is obtained by extrusion of a composite, whichcontains the components (A) and (B), and subsequent stretching. Thismicroporous foil is posttreated in a solution with molecules which haveat least two functional groups in the same molecule. One of thefunctional groups in the molecule has a positive charge, preferably thisis a positively charged nitrogen atom. The positively charged nitrogenintercalates in the layer structures or framework structures of thesilicate. A cation exchange takes place. A nitrogen cation also resultsfrom protonation of a primary, secondary or tertiary nitrogen e.g. bythe acidic silicate which intercalates into the silicate. The cationexchange at the silicate can, as mentioned already further above, takeplace completely or partly. The resulting membrane is for certainmembrane applications as alkene alkane separation already sufficientlysealed up. The remaining functional group not intercalated in thephyllosilicate or tectosilicate can be a precursor of an ion conductinggroup. For example sulfonic acid chlorides, carbonic acid chloride orphosphonic acid chlorides. Further examples of precursors of cations oranion exchange groups are given above. These precursors are converted infurther posttreatment in a group supporting the selective permeation.E.g. this is a hydrolysis in the case of the sulfonic acid halides whichtakes place in the acidic, neutral or alkaline medium. To seal the filmup further, the stretched film is now alternatingly spiked with amultivalent metal salt, e.g. Ti⁴⁺, Zr⁴⁺, Ti³⁺, Zr³⁺, TiO²⁺, ZrO²⁺, andan acid, which can be low or high molecular. As acids phosphoric acidand sulphuric acid diluted with water are particularly preferred.

The phosphoric acid has a concentration of 1-85% by weight. Preferred isa concentration from 20 to 80% by weight. The sulphuric acid has aconcentration from 1 to 80% by weight. A concentration from 20 to 50% byweight is preferred. The process of precipitation of a hardly solubleproton conductor in the membrane can be repeated severalfold.

Any substance can be used as an inorganic component which on stretchinghas the consequence that free cavities form around this substance (seeillus. 1: Process of the cavity formation by stretching). It is notmandatorily necessary either that the component must be inorganic. Theonly condition, as said already, is that void space has formed aroundthe particle after the stretching. The stretching can be carried outmonoaxially or also biaxially. A biaxial stretching is preferred. Forthe application in hollow fibers, however, a monoaxial stretching issufficient.

Additionally stretching is possible also over the third direction inspace, that is triaxially. For this purpose e.g. the composite extrudedto the film is hold level above vacuum nozzles and a plate which alsocan draw a vacuum through small pores touches down from above. The filmis now fixed between two plates. If one pulls the two plates out of eachother under applied vacuum and chooses the distance such, that the filmdoes not break but stretches only, a film is obtained that was stretchedin thickness.

Further application finds the invention in electrodialysis.

The microporous stretched membrane consists of a cation exchanger andthe second path consists of an anion exchanger, if necessary with protonleaching, e.g. as described in DE 19836514 A1 (Illus. 3; Drawings page2). Is this membrane is placed in an electrical field, the water in itdissociates into protons and hydroxyl ions. The protons move along thecation exchange path to the cathode and the hydroxyl ions (OH—) movealong the anion exchange path to the anode in accordance with theelectrical field. This way membranes can be established veryeconomically and simply for electrodialysis.

However, the paths also can be exchanged. An anion exchange membrane ora chemical precursor of the anion exchange group is then stretched firstand the second path is now a cation exchange membrane. The modificationof the inorganic component must be chosen correspondingly.

An advantage of the invention has been mentioned only briefly before.Ionomers can not be extruded as a rule. So Nafion cannot be extrudedwithout plasticisers. The plasticiser (aid to the extrusion) is latervery difficult to remove from the membrane. However, this is necessaryfor the operativeness of the membrane.

Organically modified particles (e.g. montmorillonite) can be processedaccording to the present invention in fusible and therefore extrudablepolymers to films. In the second step the continuous path is formed bythe stretching and then filled with the ion conductor.

By particle-shaped inorganic layer structures or framework structurescontaining the component (B) an otherwise under the applicationconditions of a membrane mobile or volatile functional groups carryingchemical substance of the general formula for hydrophobizationfunctionalization agents (I) or (II) is fixed in the microporous filmover a technically applicable time period so that it can be used formembrane applications.

This allows an enormous reduction in the production costs. Large areasof a “rawly” membrane can be produced in large existing plants, whichare modified depending on the application in a second step. So membranesare very economically producible according to this procedure for thedesalination of sea water. E.g. polypropylene is used as a basic polymerhere. The inorganic component, e.g. montmorillonite, is modifiedorganically before such that a charged group remains at the surface.E.g. this can be done with an alpha-omega amino sulfonic acid. After thestretching a loaded micro porous membrane results. This is suitable forreverse osmosis.

Furthermore cross-linking reactions can still be carried out within thepores through endstanding groups of the functionalization agents capableof crosslinking. This can be a covalent and/or an ionic cross-link.

Another application is the use in the alkene alkane separation.

Nitrogen in heterocycles with a free electron pair forms with silverions, e.g. silver nitrate solution, a hardly soluble complex. It has nowbeen found surprisingly that if this complex is located in a membrane,it is capable to bind alkenes reversibly.

A film is made from polybenzimidazole and soaked in a diluted toconcentrated silver salt solution, preferred is silver nitrate, over aperiod of 24 hours up to two weeks, then this membrane has a separationefficiency on alkene alkane mixtures. As a solvent for the silver saltwater or an aprotic solvent can be used. Alkenes and olefines permeatethrough such a membrane anhydrously with a technically applicable flowrate. An improvement in the flow number is reached by insertion oforganically modified montmorillonite with heterocyclical nitrogen on thesurface, bearing at least a free electron pair, e.g. an endstandingimidazole group. The membrane is stretched carefully and soaked afterthis in silver salt solution. By the stretching channel structures whichmake the transport easier are produced in the membrane.

A considerable cost reduction is obtained if a unmodified polymer, e.g.polypropylene is stretched with organically modified montmorillonite.The montmorillonite carries again endstanding imidazole or pyridinegroups on its surface. After the stretching the microporous membrane issoaked in a silver ion containing solution. After this the membrane issuitable for the alkene alkane separation. The membrane is suitably forthe separation of low molecular substances, of which one component ofthe mixture contains a double bond, which forms a reversible complexwith silver ions. The separation of low molecular olefine/alkanemixtures is particularly preferred.

The montmorillonite does not have to be modified compulsorily.Polypropylene is compounded with montmorillonite and stretched. Afterthis the porous film is posttreated with a solution containing aromaticnitrogen bearing at least one free electron pair. The solvent can be anysuitable solvent or solvent mixture. Water and aprotic solvents arepreferred. It is only important that the corresponding moleculecontaining nitrogen penetrates into the cavities of the clay and fillsout the pores. In the following step the membrane is posttreated in asilver or copper ion containing solution. Any solvent is suitably thatholds silver ions or copper ions in solution. Particularly preferred iswater and aprotic solvents such as DMSO, NMP and THF. As a consequencethe nitrogen silver ion complex or the nitrogen copper ion complexprecipitates in the membrane. This process can if necessary be repeatedseveralfold. The membrane is now suitable for the anhydrous alkenealkane separation.

1. A membrane formed by a process which comprises: providing a foilcontaining 20 to 98% by weight of a polymer component (A) and 80 to 2%by weight of a particle component (B), which comprises phyllosilicatesor tectosilicates distributed in the matrix of the polymer component (A)and having a mean particle diameter of 0.1 to 15 μm; stretching the foilmonoaxially or biaxially to provide cavities in the foil; filling thecavities using a process that includes replacing the cations of thephyllosilicates or the tectosilicates completely or partially by organicfunctionalizing hydrophobization agents and post-treating withphosphoric acid to fill the cavities in the foil.